How to copy current user'id to a custom field when adding a new entity?

Question

I have a custom content entity 'service' created with Drupal Console (drupal generate:entity:content).
I added my own fields to the standard ones created by DC. Of which 'seliste_id':

$fields['seliste_id'] = BaseFieldDefinition::create('entity_reference')
  ->setLabel(t('SEListe'))
  ->setSetting('target_type', 'person')
  ->setSetting('handler', 'default');

By default, the code generated by DC handles the owner of any new entity, owner_id being the id of the current user.
By design, seliste_id is the id of the other entity 'person' which is linked 1 <-> 1 to Drupal's 'user'.
So when a new 'service' is created, I'd like to "copy" its owner (i.e. the current user's id) to 'seliste_id'.
I know that I can do that in mymodule_entity_presave().
Is there a way to do that in the definition of 'seliste_id' field?
With ->setDefaultValue() or ->setDefaultValueCallback() maybe?
Any idea?

Answer 1

From the node entity:

$fields['uid'] = BaseFieldDefinition::create('entity_reference')
  ->setLabel(t('Authored by'))
  ->setDescription(t('The username of the content author.'))
  ->setRevisionable(TRUE)
  ->setSetting('target_type', 'user')
  ->setDefaultValueCallback('Drupal\node\Entity\Node::getCurrentUserId')
  ->setTranslatable(TRUE)
  ->setDisplayOptions('view', [
    'label' => 'hidden',
    'type' => 'author',
    'weight' => 0,
  ])
  ->setDisplayOptions('form', [
    'type' => 'entity_reference_autocomplete',
    'weight' => 5,
    'settings' => [
      'match_operator' => 'CONTAINS',
      'size' => '60',
      'placeholder' => '',
    ],
  ])
  ->setDisplayConfigurable('form', TRUE);

// ...

public static function getCurrentUserId() {
  return [\Drupal::currentUser()->id()];
}

Answer 2

Using the advice (thanks @Berdir), I tried this and it worked!

// ----------------------------------------------------------------------------
  public static function baseFieldDefinitions(EntityTypeInterface $entity_type) {
    $fields = parent::baseFieldDefinitions($entity_type);
// ----------------------------------------------------------------------------
some fields...
// ----------------------------------------------------------------------------
    $fields['seliste_id'] = BaseFieldDefinition::create('entity_reference')
      ->setLabel(t('SEListe'))
      ->setSetting('target_type', 'person')
      ->setSetting('handler', 'default')
      ->setDefaultValueCallback('Drupal\sel\Entity\Service::getCurrentUserId');
// ----------------------------------------------------------------------------
some other fields...
// ----------------------------------------------------------------------------
    return $fields;
  }

  public static function getCurrentUserId() {
    return [\Drupal::currentUser()->id()];
  }

}